1. Field of the Invention
The present invention relates generally to the field of fluid dynamic bearings and more particularly to etching grooves in a hub used in a spindle motor of a disk drive to form such bearings.
2. Description of the Related Art
Conventional disc drives use magnetic properties of materials to store and retrieve data. Typically, disc drives are incorporated into electronic equipment, such as computer systems and home entertainment equipment, to store large amounts of data in a form that can be quickly and reliably retrieved. The major components of a disc drive include magnetic media, read-write heads, motors and software. Motors, which are used to spin media at several thousand revolutions per minute, are constructed to spin with minimal vibration and to be reliable and efficient. One of the ways this is done is by insuring proper lubrication of critical moving components in the motor with oil. Proper lubrication of a motor is typically achieved by incorporating grooves in the bore of the hub and shaft through cutting processes such as electrochemical machining (ECM) processes. The bore is defined as the inner surface of the hub. Since these grooves are important for maintaining proper oil circulation, erosion of the groves can cause improper oil circulation leading to motor failure because of lockup. Therefore, measuring and understanding the erosion of the grooves in the bore and shaft is important to building a motor robust enough for hard drives.
The cutting process may be performed in any of various electro-erosive machining modes. In electrical discharge machining (EDM), the cutting liquid is dielectric liquid, e.g. deionized water, and the machining electric current is supplied in the form of a succession of electrical pulses. In electrochemical machining (ECM), the cutting medium is a liquid electrolyte, e.g. an aqueous electrolytic solution, and the machining current is a high-amperage continuous or pulsed current. In electrochemical-discharge machining (ECDM), the liquid medium has both electrolytic and dielectric natures and the machining current is preferably applied in the form of pulses, which facilitate the production of electric discharges through the conductive liquid medium.
The work piece may be disposed in a bath of the cutting liquid medium to immerse the cutting region therein. More typically, however, the cutting zone is disposed in the air or ambient environment. Advantageously, one or two nozzles of a conventional design are disposed at one or both sides of the work piece to deliver the cutting liquid medium to the cutting region disposed in the air or immersed in the liquid medium. The cutting liquid medium is conveniently water as mentioned, which is deionized or ionized to a varying extent to serve as a desired electro-erosive cutting medium.
Since modern hard drives require smaller and faster motors having finer critical features, there is a real challenge in both making and measuring the finer features made using these ECM processes and the like. For example, smaller motors have correspondingly smaller and finer groves built into their bores and shafts than ever before. The ECM process is generally known in the art. However, the ECM process raises the need to accurately and simultaneously place grooves on a surface across a gap that must be accurately measured. Deficiencies in mechanical tolerances may cause misalignment of the electrode with the work piece, causing an uneven gap and correspondingly uneven depth hydrodynamic groove. Accurate measurement of these grooves is needed to understand their wear patterns and ultimately design and build better motors. Conventional methods used to measure component wear in motors are inadequate for measuring the small dimensions found in modern bore and shaft grooves because they were developed for measurements of larger features.
Therefore, what is needed is a system and method which overcomes these deficiencies and enables measuring fine features, such as groves, on the bore and shaft of motors.